Thanks for the pictures and measurements.
The external wheel face to face of a P4 wagon wheel axle is 20.60mm, which will be a bit tight!
I notice that the Bachmann axles are a lot larger in diameter than P4 wagon axles so some new machined axles will be called for.
I think that the crane might not wish to run with such tight tolerances after modification, and or grinding out the inner faces of the main chassis molding.
All in all, a very nice model, but not one I am prepared to have to 'butcher' having paid £200+ for!
Again thanks for your help in providing some photos